In order to study charge trapping and transport in polyimide, we have submitted
samples of Kapton HN to corona charging and measured its surface potential decay
with an electrostatic voltmeter. We propose a two terms mobility to explain the
experimental data: a non dispersive contribution based on Toomer and Lewis model
added to a dispersive process, which is associated with the disordered structure
of the material. The non-dispersive model alone did not fit well to the data for
short times, but our assumption makes the theoretical expresion fit succesfully to
the experimental data. Some important parameters related to the charge transport
properties of the material are determined and discussed.